Tagged Questions

A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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3
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1answer
31 views

When does an unpaired test result in higher p-value than a paired test?

I determined some parameter in a group of subjects under two conditions, such that each subject was tested in both conditions. I want to know if the condition has an effect on the parameter. My design ...
2
votes
1answer
42 views

Asymptotic distribution of a recursive statistic

I have a (time series related) test statistic which is asymptotically normal. I would like to know what is the asymptotic distribution of its maximal value obtained by a recursive estimation. For ...
0
votes
1answer
35 views

Statistical test of stock returns product

Say I have a sequence of stock returns: $X_1, ..., X_n$. Then I make a sample of products: $X_1X_2, X_2X_3, ..., X_iX_{i+1},..., X_{n-1}X_n$ How to test, if the sample mean is significantly different ...
0
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0answers
34 views

Advice on research study

I am collecting data on extroversion using a personality scale at a clinic. I have about 50 subjects where 15 are in experimental group receiving interventions. I am also collecting data on ...
0
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0answers
8 views

Using t-test for feature selection after z-scoring data?

Suppose I have a high-dimensional dataset, and a binary classification problem. I want to use the two-sample t-test for feature selection. If the data has been normalized by z-scoring (so it has zero ...
1
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0answers
22 views

Statistical test: Does actual time series data deviate from forecast?

I have made a prediction of future sales based on an ARIMA model. The ARIMA model is based on past data, during which there has been no marketing activity. During the period predicted by ARIMA, I will ...
0
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0answers
12 views

A/B testing zero inflated data

I am trying to conduct an A/B(/C) test to compare the performance of 3 different website pages but I'm facing issues regarding zero inflated data. I have data for each page regarding ...
1
vote
1answer
49 views

Best way to compare pre vs post levels in treatment vs control groups?

In a study, drug was given to tt (treatment) group and not to cc (control) group and blood levels of (say) cholesterol were tested before and after in each subject. I have following data: ...
0
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0answers
17 views

p-value test for comparing classifiers

I have to use p-value test to compare two classifiers. I am getting the error vectors of 2 hypothesis and I am using their difference as an input in ttest function of MATLAB ...
1
vote
1answer
20 views

math explanation for using paired-t

Not a math/stats person, but I am interested in finding out why "paired t" would be a preferred test for samples that are not "independent". I googled a bit on this topic, but didn't really find ...
0
votes
1answer
48 views

Calcuate Bayes Factor for Adjusted Mean Difference

I have an ANCOVA model shown below (fit) where I calculated the mean difference between two groups while controlling for another variable (x). For the adjusted mean difference (288.72), I'd like to ...
3
votes
1answer
40 views

Independent/Dependent variables & type of statistical test

If someone is investigating differences in means between 2 groups, does it matter which we consider to be the IV and the DV? For example, can I use a t test to examine the difference in the age of ...
2
votes
1answer
35 views

hypothesis test for a boolean combination of alternatives

I have a student (for a high school project) who has conducted an experiment and collected data in the following (simplified) way: id|situation|scoreX|scoreY ...
3
votes
2answers
30 views

Is paired t test sufficient to show the two data sets are similar

Let me give the details of my problem setting, we have a learning algorithm that can take a collection of algebra problems and automatically generate similar ones. Of course, an important question to ...
0
votes
0answers
7 views

Comparing two sample means (t-test) [duplicate]

In a t-test of two sample means, with 2 degrees of freedom, the t-stat = -14.55. The two-tail significance is 4.30. My question is, is the t-stat significant? And, the t-stat seems to be ...
0
votes
0answers
12 views

comparison of time values as response variable

The data set I have is a 12 subject Latin Square cross-over design with 2 periods (1 or 2), 2 sequences (AB OR BA) and 2 drug formulation treatments (A or B). The subject response variable is a time ...
2
votes
0answers
37 views

Which statistical test for women height?

Suppose women may have Blue or Red eyes. We make a first cheap research on a 100 women checking just one eye of each woman. So after the research we have results: At least one eye Blue have avg ...
1
vote
1answer
46 views

How to describe three groups where the means of two groups are significantly different, but neither of the two groups differ from a third group?

I am comparing 3 means from normal distributions using student's test: $\mu{_1}, \mu{_2}, \mu{_3}$ Results are: $\mu{_1} = \mu{_2}, \mu{_2} = \mu{_3}, \mu{_1} \ne \mu{_3} $ If I want to group my ...
2
votes
1answer
30 views

Testing if a interval scaled variable A and a nominally scaled variable B are independet when A is not normally distributed

We have a variable A which denotes a percentage between 0 and 1. The variable is not normally distributed but has a very left skewed distribution. About 5% of the observations are zero, most ...
2
votes
3answers
70 views

Can I do a t-test to test significance? [closed]

I need a statistical test to determine if one group of ten classrooms with different numbers of students in each class has a class average on a test. Group two has 12 classrooms also with different ...
1
vote
1answer
29 views

Is this a case of multiple-test?

I had a different view with a friend on whether we need an adjustment of p.values for multiple tests. Here is the case, we have a compositional data set with $n=1000$ subjects and $m=26$ continuous ...
3
votes
2answers
60 views

Empirical rejection rate of a wrong null hypothesis -is it the “power of the test”?

I guess this is basic, but it forms part of the holes in my statistics education. What I know is that the power of a hypothesis test is not a fixed magnitude, but a function of various factors ...
0
votes
1answer
43 views

Using 2 sample T test in time series data

I have two data series (not stationary) and I would like to see if the mean of series 1 is significantly different when a certain condition (on the other series) is met. The theory is that when ...
1
vote
2answers
45 views

Hypothesis testing: difference between proportions

I am investigating staff inequality between genders and ethnicities in an institution. I have data on contract types (permanent or fixed term) and pay grades for almost all employees. I want to test ...
0
votes
0answers
17 views

Degrees of freedom for a t-test using multiple imputation

I ran a paired samples t-test using multiple imputation in SPSS, and I am unsure as to how to proceed in reporting the degrees of freedom from the pooled data. The original data had 43 df and now it ...
0
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0answers
278 views

Calculate at .05 level of significance

A research organization claims that the monthly wages of industrial workers in district X exceed those in district Y by more than Rs 150. Two different samples drawn independently from the two ...
0
votes
1answer
24 views

Wilcoxon Rank Test or T-Test? [duplicate]

What data analysis is better? or fit for my data? I've used Likert scale for my questionnaire (1-5) and I have 387 respondents. Wilcoxon Rank Test or T-Test?
0
votes
0answers
21 views

T-Test using MPlus

Is it possible to perform a paired samples t-test in MPlus? I am confused, as I have found on the web that you can run a wald test, but I am not sure if it is the same as a t-test. The reason I want ...
1
vote
1answer
26 views

Statistical test for power law samples

What is the t-test analog for testing against the null hypothesis that two samples come from the same distribution, if the two samples are distributed according to power law and have different number ...
4
votes
1answer
58 views

Reporting t-tests instead of simple linear regressions

Many papers in health research based on observational data use the following format: Does A cause B? t-test A vs B (or chi-square, or whatever other test of dependence between two variables) ...
3
votes
3answers
839 views

Why there is no significant difference between a number list and its 100 times list

I am finding that there is no significant difference between a number list and another list which has 100*same numbers. The P value is 0.4487. The means are obviously very different (100 times). Why ...
1
vote
1answer
44 views

Effectsize difference between Mann-Whitney U and t-Test

I have data that is officially not normally distributed (Kolmogorov-Smirnov test < .000 BUT N=around 1200 so K-S not really reliable). In plot I can see that form looks good but negatively skewed. ...
0
votes
1answer
27 views

Can I use independent t-test for my sample? [duplicate]

I want to compare the means of two independent variables, but my problem is the large difference in their sample sizes. One of my variables consists of 560 people and the other only has 29. So can I ...
4
votes
1answer
113 views

I just don't get the t-test

I know it sounds abysmally ignorant, but here we go. I understand the basic logic behind the t-test: you want to know whether the difference in the mean of two samples is due to chance or not. To ...
0
votes
0answers
30 views

Welch t-test: Exactly when should it be used? [duplicate]

The guidance on this site concerning when to use the Welch t-test is somewhat general in nature (When conducting a t-test why would one prefer to assume (or test for) equal variances rather than ...
1
vote
2answers
168 views

Why do we have to assume normality for a one-sample t-test?

As a consequence of the central limit theorem the sampling distribution of the sample means will always be normal whatever is the distribution of the variable we measure. From our sample we can ...
4
votes
2answers
64 views

Effect size for a one-sample t-test

Imagine I work in a screw factory (which is not true). We have been producing a series of 5cm-long (on average) screws for years. I want to modify the production parameters in order to save some money ...
9
votes
2answers
235 views

Explanation for non-integer degrees of freedom in t test with unequal variances

The SPSS t-Test procedure reports 2 analyses when comparing 2 independent means, one analysis with equal variances assumed and one with equal variances not assumed. The degrees of freedom (df) when ...
0
votes
0answers
46 views

two samples, hypothesis test of proportions t or z test

I have two samples of documents where one sample contains documents of a certain category and another sample contains documents of another category. I am analysing the occurrence of a certain word in ...
0
votes
1answer
31 views

Running many $t$-tests to find the most significant way to divide a dataset

I apologize for my stats illiteracy in advance–I'm not a stats guru by any stretch, but am trying to learn. To start, I'll just introduce what my data set looks like, then what I'd like to ...
2
votes
1answer
26 views

Compare group mean to larger group of which it is part

I have thousands of evaluation scores, over several sites, which vary in number of evaluations for each. I am tasked with comparing the evaluation means for each site to the all-site mean. The ...
0
votes
2answers
36 views

Beyond a Welch's t-test

I have two groups of species: the groups have different numbers of species. For each species, a different number of individuals have been screened for a gene. I want to describe the difference for ...
0
votes
1answer
39 views

Wald test on marginal effect

Say I have the following regression equation: $$Wage_i = YearsOfEduc_i + Age_i + NumOfSiblings_i + u_i$$ How would I go about peforming a wald test of the hypothesis that for an individual with ...
3
votes
0answers
10 views

Significance test for longer pronounciation

I have a set of words spoken by a group of native speakers and a group of non-native speakers. In each record I determined the length of the burst (a phonetic term). I believe non-native speakers tend ...
2
votes
1answer
81 views

Confidence Intervals Around a Mean: biased (non-centered) confidence interval? (an exercise using R)

I've been playing around with the module "Confidence Intervals Around a Mean" (meanCI) from statsTeachR (www.statsteachr.org), authored by Eric A Cohen (unfortunately, author's contact information was ...
3
votes
1answer
108 views

Is Student's t test a Wald test?

Is Student's t test a Wald test? I've read the description of Wald tests from Wasserman's All of Statistics. It seems to me that the Wald test includes t-tests. Is that correct? If not, what makes a ...
1
vote
2answers
43 views

If one group has 23 participants and the second group has 117 participants in it, can we rely on the result of t-test? [duplicate]

I was evaluating a research paper in which the authors have 23 male participants and 117 female participants. They have applied t-test to calculate Gender differences and have even concluded on ...
1
vote
1answer
43 views

What statistic to use

My 8 year old daughter is conducting an experiment to assess memory. She has 3 groups. Condition 1, Condition 2 and ...
0
votes
1answer
14 views

What should I use to run a pre and post after intervention with a control group 15 participants?

I want to know the effect of reflective video analysis on teacher intentions to stay or leave the teaching position, teacher efficacy, and teacher job satisfaction in rural middle schools. I will ...
1
vote
1answer
36 views

When testing for a difference between effect sizes, is test power affected by their respective magnitude?

When comparing two effect sizes with a statistical test, does it matter for the test's power whether these effect sizes themselves are large or small? Imagine you are planning an experiment in which ...